(Answered) Physical combat (mostly between 'Mechs in Depth 1 water)

[Alfaryn]

Reading this thread:
https://bg.battletech.com/forums/total-warfare/physical-attacks-against-quad-mechs-in-depth-1-water/
the threads linked in it, and BMM (pp. 26, 35, 64-65), TW (pp. 102, 107-108, 144), and AGoAC rulebook (pp. 17, 19 and 25) leads me to believe that there are a few problems with the rules regarding physical combat. Most of the problems seem to occur during combat between 'Mechs standing in Depth 1 water.

1. Kick Attacks. According to p. 35 BMM "For a standing biped ’Mech, Depth 1 water provides partial cover against any physical attack that does not roll on the Punch Location Table [...]", which would mean that a kick attack between two 'Mechs standing in Depth 1 water would be subjected to a +1 to-hit penalty for partial cover. One of the old rules answers (https://bg.battletech.com/forums/total-warfare/answered-bmm-water-providing-or-not-providing-cover-to-physical-attacks) and p. 25 of the AGoAC rulebook explicitly disagree - according to them the attacking 'Mech to-hit penalty. As far as I can tell TW does not address this situation explicitly, but the general rules for partial cover in this book are written in such way, that I think that according to TW the attack would qualify for a +1 to-hit modifier.

So I guess we need corrections in at least one book to cover this case (my guess is BMM, and possibly TW)?

At least all sources seem to agree here that a successful kick would deal half of the standard damage (rounded down)...

2. Physical Weapon and charge attacks. Even worse, the following paragraph p. 35 BMM reads "If partial cover applies, resolve the physical attack’s hit location as normal. However, if the attacker is at Level 0, any damage grouping that resolves to the legs is ignored. If the attacker is instead in water of Depth 1 or deeper, any damage grouping that resolves to any location except the legs is ignored.", which would mean that a physical attack that uses regular Hit Location Table (like a charge or most physical weapon attacks) would not only suffer a +1 to-hit, but all damage groupings from such attacks that did not hit target's legs would be ignored, which doesn't make sense to me. According to p. 25 AGoAC rulebook such attacks would suffer a +1 to-hit penalty, but unlike BMM would be able to damage any part of a 'Mech except legs (which seems fine for physical weapon attacks, but not necessarily for charge attacks). Same thing seems to be the case under TW rules.

Which rules (if any) are correct here? My guess would be that charge attacks shouldn't suffer any penalties for partial cover (no +1 to-hit modifier, no damage groupings striking cover instead of target 'Mech (or the attacking 'Mech)), while physical weapon attacks that use regular Hit Location Table should suffer typical penalties for partial cover (+1 to-hit, and all damage groupings to the legs ignored).

3. Amount of damage dealt. The rules in all books are also unclear about amount of damage that would be dealt in such situation - would such attacks be considered as "beginning under water", which would mean the damage from it is halved (see pp. 35, 65 BMM, 144 TW), or not? For physical weapon attacks I would guess "not", but I wouldn't be so sure about charge attacks, though at the same time I think that damage from underwater charge attacks probably shouldn't be halved regardless of depth at which they happen, since in case of 'Mechs the increased MP cost for moving them through water already reduces damage potential of such attacks, while at the same time I fail to see a reason to halve charge attack damage from units that can actually move quickly on or under water (like naval vessels or hovercraft) compared to charge attack damage done by units with the same mass moving at the same speed outside of water. Another problem with halving damage from charge attacks is that it rises additional questions not covered by the rules, like "Is damage to the attacker also halved?" or "Is only the damage to the legs, not torso, head or arms, halved?"

4. Attacks from Depth 2. Finally there is a case where a 'Mech standing at depth 2 attacks a 'Mech standing at depth 1 (assuming that water surface at both adjacent hexes is at the same level). According to Different Levels Table (pp. 34 BMM, 150 TW, 25 AGoAC rulebook) all physical attacks possible in this situation (except charge) use Kick Table, which according to all three rulebooks would mean that the target 'Mech would get partial cover, the damage from attacks would be halved, and could only strike the legs. The only problematic attack is a charge - according to p. 26, 35 BMM, 108 TW, (but not according to AGoAC rulebook) any damage from such charge attacks striking any part of the 'Mech other than legs would be ignored. Doesn't seem logical to me for reasons similar to the ones I've mentioned in point 2., especially since Different Levels Table instructs players to use regular Hit Location Table regardless of which 'Mech (if any) is standing higher prior to attack, which makes me think that the rules' intent is that charge attacks should be resolved as if the attacker entered the target's hex (and, as a consequence - level) first, and only aferwards collided with the target.

5. Quick reccomendation. Aside from the changes suggested in the previous points, I think that the sentence "If the attacker is instead in water of Depth 1 or deeper, any damage grouping that resolves to any location except the legs is ignored." on p. 35 BMM should be scratched from the book, because if both the attacker and the target are on Depth 1 I see no reason why physical attacks other than kicks wouldn't be able to hit 'Mech locations other than legs (if anything it is the legs that IMO should be protected from some attacks - as discussed above), and if the attacker is at Depth 2 all possible physical attacks other that charges may only hit target's legs anyway because they use Kick Table to resolve hit locations, while charge attacks should be able to hit any part of target 'Mech anyway. So in every possible case the sentence in question is either wrong or redundant.
By the way on official maps water level on two adjacent hexes isn't always at the same level (see Large Mountain #1 and LOS diagrams derived from it - pp. 100 TW, 23 BMM, 14 AGoAC rulebook), - a situation which comes with its own problems when resolving physical attacks, but I think that we can leave these for another thread. 
There is also another small issue that I noticed while working on this post - "Water" paragraph in Partial Cover Modifier section of p. 26 BMM is worded in such way that it may suggest that attacks striking Torso, Head or Legs of a 'Mech standing in Depth 1 water strike cover instead only if they are made by a fully submerged 'Mech, which aside from all problems with physical attacks mentioned above isn't even always true for weapon attacks - leg mounted weapon attacks are resolved like that even when they are fired by partially submerged 'Mech. This case is explained on p. 64 BMM, but should probably be also mentioned on p. 26 BMM.

[Xotl]

Okay, let's try a test run, using AGOAC as the base.  I'm thinking of replacing the Physical Attacks and Water section of AGOAC, p. 25, with the following:

   

   Damage resulting from physical attacks is halved when applied to an underwater location (round down).
   Target Partially Submerged: A standing ’Mech in Depth 1 water has its legs submerged. This gives it partial cover (see p. 17) against physical attacks, except those that use the Punch Location Table. Bear in mind that the attacker and target being at different levels can change what location table an attack uses (see the Different Levels Table below). For example, if a ’Mech at Level 0 kicks a ’Mech in Depth 1 water, the kick uses the Punch Location Table and so partial cover would not apply.
   If partial cover applies and the attacker is at the same LOS level (see p. 13) as the target, a hit that does not use the Kick Location Table and resolves to the legs is ignored; charges ignore this rule.
   Target Fully Submerged: A standing ’Mech in water Depth 2 or deeper (or a prone ’Mech in water Depth 1 or deeper) is fully submerged. A physical attack cannot be made against a fully-submerged ’Mech unless the attack takes place entirely underwater.
   For example, a ’Mech standing in Depth 1 water adjacent to a prone ’Mech in Depth 1 water can only kick it, since the kick would occur completely underwater. A DFA cannot be made against the prone ’Mech because a portion of the attack would take place outside the water.

I think that works, but another set of eyes on it would be appreciated.  If it works, I can iterate it to BMM and TW easily enough I think.

[Alfaryn]

To make sure I understand the new rules correctly, here are a few examples of physical attacks by 'Mechs against other 'Mechs and how I would resolve them using the rules suggested by Xotl above. Since AGoAC doesn't deal with vehicles I'll leave the problem of charges by and attacks against them (especially Naval Vessels and Hovercraft) for now. I've also not touched the rare case where water surface of two adjacent hexes is on different levels, though once again - this situation does happen on at least one or two official maps (Large Mountain #1 and, judging from what I see in MegaMek, Kozice Valley), and I can already see some cases where the above rules could lead to weird results on such maps.

1. A 'Mech equipped with a hatchet standing in depth 1 water next to another 'Mech standing on the same level, also in depth 1 water has the following options:
  a. Attack using regular hit location table. +1 to-hit modifier for partial cover applies. If the attack would hit the legs it strikes cover instead. If it strikes any other location - full damage is dealt.
  b. Attack using punch location table. +4 to-hit modifier for choosing punch location table is applied, but not the +1 for partial cover. Full damage is dealt.
  c. Attack using kick location table. +4 to-hit modifier for choosing punch location table is applied, AND +1 for partial cover. Half damage is dealt.

2. A 'Mech charging another 'Mech standing in depth 1 water is subjected to a +1 to-hit modifier, and any damage value grouping that resolves to the legs is ignored. Full damage applied otherwise. Resolution of this attack does not depend on level and/or depth of water in the attacker's hex, except for the fact that the level of attacker's hex (level of the bottom in case of water hexes) must be within +/-1 level of the bottom of the water the target is standing in - as usual for charge attacks. The rules don't make it clear how to resolve damage suffered by the attacker in this case - would damage value groupings to the legs be applied in full, halved (rounding down to two?) or ignored?

3. A 'Mech standing in depth 2 water making a punch, club or physical weapon attack against a 'Mech standing one level higher, in depth 1 water suffers a +1 to-hit for partial cover, and deals half damage to whatever leg was hit (since these would be resolved using kick table).

4. As above, but the attacker is standing in depth 3+, and the defender is standing one level higher - in depth 2+ water. No to-hit penalty for partial cover. Half damage is applied using kick table.

5. Same situation as 3 or 4, but the target is prone. No partial cover. Half damage is applied using regular hit location table.

6. 'Mech in depth 2+ water charging a 'Mech standing in depth 2+ water. No partial cover. Half damage is applied to the target. Is half damage applied to the attacker? (In other words - does the first sentence of the rules proposed in the above post apply to the damage suffered by the attacker, or only the target?) How does halving damage work in this case? Do I halve the damage first, and then split into 5-point groupings, or split it into groupings first, and then reduce it to 0-2 points each)?

7. A 'Mech standing in depth 1 water attempting to charge a 'Mech standing one level lower, in depth 2 water. No such attack is possible, because it doesn't take place entirely underwater.

I used bold text where I either found the rules with proposed changes ambiguous, or where the results of using the proposed rules as written were IMHO weird and counter-intuitive. Note that every single one of these fragments written in bold refer to resolving charge attacks, so perhaps it would be simpler to make a rules exception for charges after all? Another thing that the rules don't seem to cover are push attacks. In most cases it is not a problem, since push attacks don't deal damage directly, and they require both 'Mechs to stand on the same level, but does a +1 to-hit modifier for partial cover apply when one partially submerged 'Mech pushes another partially submerged 'Mech?

Actually, perhaps both charge and push attacks could be covered by the same rules exception? Something like "Push and Charge Attacks: Always resolve these kinds of attacks (but not falls that may result from them or movement required to initiate them) as if no water was involved." in AGoAC, and "Push and Charge Attacks: Always resolve these kinds of attacks (but not hull breach checks or falls that may result from them or movement required to initiate them) as if no water was involved." in BMM? That is of course assuming that you find it acceptable for the rules to work that way...

One more thing - is damage applied to an underwater location supposed to be rounded down to a minimum of 0 or 1? And how does that reduction stack with damage reductions from things like damaged or missing actuators?

[Xotl]

I've also not touched the rare case where water surface of two adjacent hexes is on different levels, though once again - this situation does happen on at least one or two official maps (Large Mountain #1 and, judging from what I see in MegaMek, Kozice Valley), and I can already see some cases where the above rules could lead to weird results on such maps.

I've made a slight edit to the rules post to attempt to address this, referencing the concept of LOS level (which is mech level plus terrain level, and called out specifically in the same printing that this water correction will be added to).  If you don't think it works, please let me know.

1. A 'Mech equipped with a hatchet standing in depth 1 water next to another 'Mech standing on the same level, also in depth 1 water has the following options:
  a. Attack using regular hit location table. +1 to-hit modifier for partial cover applies. If the attack would hit the legs it strikes cover instead. If it strikes any other location - full damage is dealt.
  b. Attack using punch location table. +4 to-hit modifier for choosing punch location table is applied, but not the +1 for partial cover. Full damage is dealt.
  c. Attack using kick location table. +4 to-hit modifier for choosing punch kick location table is applied, AND +1 for partial cover. Half damage is dealt.

All correct.

3. A 'Mech standing in depth 2 water making a punch, club or physical weapon attack against a 'Mech standing one level higher, in depth 1 water suffers a +1 to-hit for partial cover, and deals half damage to whatever leg was hit (since these would be resolved using kick table).

Correct.

4. As above, but the attacker is standing in depth 3+, and the defender is standing one level higher - in depth 2+ water. No to-hit penalty for partial cover. Half damage is applied using kick table.

Correct.

5. Same situation as 3 or 4, but the target is prone. No partial cover. Half damage is applied using regular hit location table.

Correct.

7. A 'Mech standing in depth 1 water attempting to charge a 'Mech standing one level lower, in depth 2 water. No such attack is possible, because it doesn't take place entirely underwater.

Correct.

One more thing - is damage applied to an underwater location supposed to be rounded down to a minimum of 0 or 1? And how does that reduction stack with damage reductions from things like damaged or missing actuators?

Never round to less than 1 unless specifically told to do so.  Apply each damage alteration step in full before moving onto the next, including any rounding.  E.g. 7/2 = 3.5, round down to 3, then proceed to the next alteration step.  You can see this procedure in effect with the Blue Shield PFD rules in TO.  However, I'm going to add a rounding section to AGOAC to help out new players understand this.  EDIT: This is provisional, as there's a few ways to do rounding in the rules and I'll be trying to settle on something consistent.

----

I've made a very small edit to deal with charges.  While I was reluctant to add any sort of exception for them (the last thing the core rules need are more exceptions), it actually allows me to simplify some other bits and I think works overall better (though I'm at the absolute limit on that page as to what I can cram in for text).  So charges still apply the +1 like everything else (consistency) but ignore the "damage to legs is negated" rule (it would still be halved for being underwater though: again, consistency).  Take a look at the edited text and let me know if you see any issues with it.  Thanks as always.

[Alfaryn]

I don't think that the latest version of the rules you proposed is ideal, but considering space constraints I don't see how it could be written much better. Just a couple more questions that may or may not lead to more rules tweaks:

1. Are push attacks against a partially submerged 'Mech supposed to suffer a +1 to-hit penalty for partial cover, like a charges would in the same situation? Push attacks don't use punch location table, so according to the currently proposed rules they would get this modifier.

2. Is damage a charging 'Mech suffers as a result of its charge considered a "physical attack damage" and thus halved if it happens to a submerged part of the 'Mech? I guess that the answer is yes, but you may want to clarify it, if not in the "Physical Attacks and Water" section on p. 25, then somewhere in the "Charge Damage" section on p. 26.

3. How does halving underwater damage for charge attacks work exactly? I guess that damage to the legs of a partially submerged 'Mech can be handled only in one way - by reducing individual damage value groupings to 1 (from 1-3 points of damage) or 2 (from 4-5 points). But what about damage to a completely submerged 'Mech? Do I still reduce each individual grouping, or do I reduce the entire incoming damage first, and then divide it to the usual 5-point groupings? I would say it should be the latter, but it would be inconsistent with how the charge damage to the legs of a partially submerged 'Mech would have to be resolved under the rules you proposed. And since you want to avoid rules inconsistencies, perhaps you should rethink the idea of halving charge damage to the legs of a partially submerged 'Mech?

Finally, regarding rounding rules - while a rounding section in AGoAC would technically cover this issue, perhaps you may also want to consider changing all other relevant instances of "round down" to "round down, to  minimum of one"? Assuming there is enough space for it in the book of course. It would certainly make new players' lives easier. Unless I'm missing something, there are ten such instances in the book:
- p. 12, at the end of Into Water paragraph,
- p. 25 in the Physical Attacks and Water section (we already covered this one),
- p. 28 at the end of Punch Attacks section,
- four instances on p. 33 - in the Hip (Leg), Lower Arm Actuator (Arm), Lower Leg Actuator (Leg), and Upper Arm Actuator (Arm) sections. (Assuming of course that critical damage to a Hip can't bring a 'Mech to 0 MP, at least as long as it doesn't suffer MP penalty for heat. If this is not the case, then the rules should definitely say so.)
- p. 43 in the Water paragraph,
- p. 44 in the Falling 'Mech Hits Target section,
- p. 51 in the second point of the No Lower Arm Actuator list.

And sorry for the usual mess, including that punch location table in point 1.c. of my previous post.

[Xotl]

1. Are push attacks against a partially submerged 'Mech supposed to suffer a +1 to-hit penalty for partial cover, like a charges would in the same situation? Push attacks don't use punch location table, so according to the currently proposed rules they would get this modifier.

Yes, it would apply.

2. Is damage a charging 'Mech suffers as a result of its charge considered a "physical attack damage" and thus halved if it happens to a submerged part of the 'Mech? I guess that the answer is yes, but you may want to clarify it, if not in the "Physical Attacks and Water" section on p. 25, then somewhere in the "Charge Damage" section on p. 26.

Yes.  I honestly don't see how someone could claim that the damage they take from a charge is anything but physical attack damage.  That would be a particularly indefensible bit of rules lawyering; there's no special categorization for attacker vs. defender.

3. How does halving underwater damage for charge attacks work exactly? I guess that damage to the legs of a partially submerged 'Mech can be handled only in one way - by reducing individual damage value groupings to 1 (from 1-3 points of damage) or 2 (from 4-5 points). But what about damage to a completely submerged 'Mech? Do I still reduce each individual grouping, or do I reduce the entire incoming damage first, and then divide it to the usual 5-point groupings? I would say it should be the latter, but it would be inconsistent with how the charge damage to the legs of a partially submerged 'Mech would have to be resolved under the rules you proposed. And since you want to avoid rules inconsistencies, perhaps you should rethink the idea of halving charge damage to the legs of a partially submerged 'Mech?

Damage groupings are always treated as their own hit.  So break it into five-point groups as normal, and then drop each of those groups down as normal if they are applied to an underwater location.  This applies whether you're partially underwater or fully underwater.  I've made a slight edit to attempt to clarify the timing of the halving.

Finally, regarding rounding rules - while a rounding section in AGoAC would technically cover this issue, perhaps you may also want to consider changing all other relevant instances of "round down" to "round down, to  minimum of one"? Assuming there is enough space for it in the book of course. It would certainly make new players' lives easier. Unless I'm missing something, there are ten such instances in the book:

The new rounding section will say "to a minimum of 1", which is important as I can then avoid having to add it everywhere, since in several cases that would result in the sentence then flowing over to a new line and me having to then find room to cram that in.

Thank you for your feedback.  This different level stuff leads to a lot of tricky minutiae I want to get just right.  Cheers.

[Alfaryn]

Damage groupings are always treated as their own hit.  So break it into five-point groups as normal, and then drop each of those groups down as normal if they are applied to an underwater location.  This applies whether you're partially underwater or fully underwater.  I've made a slight edit to attempt to clarify the timing of the halving.

Does this also apply to situations other than physical combat, like falls underwater or into water (see p. 43 AGoAC)? If so, then hull breech rules from TW/BMM are even more scary than I thought...

[Xotl]

No, that's got its own procedure spelled out; by always I meant "always in this case" and as a general rule of damage application (as opposed to calculation; similarly, the various advanced armours do things yet another different way).

While I'd prefer to be consistent and use the same mechanics when possible, I don't want to follow the fall procedure because that can safely be assured that every location is broadly being treated the same.  Charges make it so that you can have damage dealt above and below the water line, so there isn't really a logical way of halving it right at the start, and it's not worth adding in more text/a separate procedure that goes "in the case of a charge that occurs entirely underwater...".

But yes, each damage grouping is its own hit, so hull breaches are not checked for once for a single fall but after each damage grouping application, making underwater falls quite dangerous even with the reduced damage.  I rather dislike the breach rules for that reason (well, not just that reason, but it helps).

[Alfaryn]

Got it, thanks. By the way, is it only me, or did we end up nerfing underwater charges into near uselessness? At least as long as we don't use hull breach rules, which probably make them more risky than DFAs instead. As for disliking hull breach rules - I get where you are coming from, though I personally dislike vehicle motive crits more, if for very similar reasons...

[Xotl]

Underwater charges have never been much of a tactic to begin with, since you can't run in water and you have to make a PSR for each water hex you enter.  Also, the damage halving for underwater attacks already existed; it was just badly worded.  Now at least you can potentially apply some small amount of damage to the legs in cases where the target is standing in Depth 1, rather than having that damage grouping negated altogether for being a leg hit.  So I don't think charges have meaningfully gotten weaker: there's just a better understanding of how to resolve them in the rare cases that they occur.

[Alfaryn]

I was thinking mostly about charges by units that can move relatively quickly underwater. Submarines for example. After all why would a submarine do twice as much ramming damage while surfaced then while submerged (and moving at the same speed in both cases)? In both cases it has the same momentum after all, so if anything it should do more damage underwater, due to the fact that water resistance makes it ore difficult for a rammed unit to "roll with the blow" so to speak.

I do realize that AGoAC rules don't cover submarines, but since the rules we are discussing here are supposed to be a prototype for changes in BMM and TW down the line, I think we should keep them in mind. Otherwise we my end up with nice, concise rules that work for 'Mechs, but at the same time require exceptions to handle other kinds of units well, and that would just be pushing the problem to a different place in TW, which is something we should avoid in my opinion.

As for charges by 'Mechs (including the depth 1 case), I would say that halving charge damage, unlike damage from other kinds of physical attacks, makes little sense to me - mostly because it basically means applying the penalty twice. Damage of all other physical attacks doesn't depend on attacker's speed, so it makes sense to reduce it to account for the fact that the attacker needs to overcome water resistance to punch, kick, etc., but damage of a charge attack depends on number of hexes traveled, and in most cases a 'Mech can't nearly as quickly quickly in water as on land - both because it has to pay extra MP to enter water hexes, and because it can't run while doing so. Consider a charging 8/12 MP Locust for example. If it makes a "perfect", straight charge on clear, flat land, it can do at most:

11 (hexes traveled while running, not counting 1 MP for entering target hex) * 2 (tonnage/10) = 22 points of damage.

The same Locust charging once again mostly on clear, flat land, only with a target in depth 1 hole filled with water can do at most:

5 (hexes traveled while walking, not counting 3 MP for entering target hex) * 2 (tonnage/10) = 10 points of damage (about 45% of the maximum potential damage on land) even before any reduction of the leg damage.

In other words even in such ideal conditions need a 'Mech faster than a Locust to be able to deal more than 50% of your maximum land charge damage while charging into water, even before applying damage reductions for damage groupings that strike underwater locations. And if I want to charge a 'Mech at depth 2, cross more water hexes along the way, have even 1 hex side turn to line up the charges, etc., the situation tends to end up even worse for the 'Mech trying to charge a target in water, compared to a 'Mech charging entirely on land...

By the way, note that under current rules proposal the way rounding damage works with underwater charges damage from them can easily end up closer to something like 40% of the damage before reduction (in worst case scenario even 33%, though I doubt many would attempt that particular charge even without damage reduction), which is yet another part of the reason why I said that we've made them nearly useless.

The more I think about this whole problem, the more I'm convinced that not making a rules exception for charges (and possibly pushes) has two big downsides:
- it leads to unrealistically low damage from underwater charges by submarines, at least when compared to charges by the same submarines while surfaced, not to mention ridiculously low damage by charging 'Mechs (even in ideal conditions for such attacks) - as discussed above,
- it creates an exceptional way of resolving damage in reduced 1-2 damage value groupings that only applies to charges, not to mention the explicit exception about partial cover not blocking damage to the legs from charge attacks.
In my opinion adding "The following section does not apply to Charge Attacks." (or "[...]Charge and Push Attacks.") and scratching "[...] charges ignore this rule." from the rules you proposed would be less problematic, even if it may look less elegant at first glance. And the game balance wouldn't really change - 'Mech charges in water would still do little damage, and both Vehicle and 'Mech charges would be risky for the attacker with hull breach rules, so I don't think we would see many of them even without halving damage to underwater locations or +1 to-hit modifier at depth 1.